Sayaka Kotegawa

She is Chisa and Nanaka's mother and the manager of Dophin diving pad at Palau, where Chisa, Iori, Kouhei and Aina work part-time during summer break. Sayaka is a serious and straightforward person, who doesn't talk beyond what is necessary and acts cold towards Chisa. She is deaf in her left ear, because of constantly ear pressure during diving, and never told Chisa because she knows how much she loves diving.